DISTRIBUTION AND SOURCES OF PRE-ANTHROPOGENIC LEAD ISOTOPES IN DEEP-OCEAN WATER FROM FE-MN CRUSTS

The lead isotope composition of ocean water is not well constrained du e to contamination by anthropogenic lead. Here the global distribution of lead isotopes in deep ocean water is presented as derived from dat ed (ca. 100 ka) surface layers of hydrogenetic Fe-Mn crusts. The resul ts indicate that the radiogenic lead in North Atlantic deep water is p robably supplied from the continents by river particulates, and that l ead in Pacific deep water is similar to that characteristic of island and continental volcanic area. Despite a short residence time in deep water (80-100 a), the isotopes of lead appear to be exceedingly well m ixed in the Pacific basin. There is no evidence for the import of Nort h Atlantic deep water-derived lead into the Pacific ocean, nor into th e North Indian Ocean. This implies that the short residence time of le ad in deep water prohibits advection over such long distances. Consequ ently, any climate-induced changes in deep-water flow are not expected to result in major changes in the seawater Pb-isotope record of the P acific Ocean.